As a marking pen ink for writing board, there has heretofore been commonly used a volatile organic solvent-based ink. In recent years, various compositions of aqueous ink have been proposed in the light of odor and safety in use, as disclosed in JP-B-6-4805, JP-B-8-16206 and JP-B-8-32845 (The term "JP-B" as used herein means an "examined Japanese patent publication"). Writing drawn by these prior ink can be fairly erased after completely dried. However, as compared with writing drawn by a volatile organic solvent-based ink, writing drawn by an aqueous ink on a writing board dries slowly and therefore it is often erased in a half-dried condition. In such a case, staining of the entire surface of the writing board with the ink occurs, which tends to cause insufficient erase.